We present a Gallium Nitride (GaN) Lamb Wave resonator using a Phononic Crystal (PnC) to selectively confine elastic vibrations with wide-band spurious mode suppression. A unique feature of the design demonstrated here is a folded PnC structure to relax energy confinement in the non-resonant dimension and to enable routing access of piezoelectric transducers inside the resonant cavity. This provides a clean spectrum over a wide frequency range and improves series resistance relative to transmission line or tethered resonators by allowing a low-impedance path for drive and sense electrodes. GaN resonators are demonstrated with wide-band suppression of spurious modes, f -Q product up to 3.06 x 1012, and resonator coupling coefficient k2.eff up to 0.23%. (filter BW up to 0.46%). Furthermore, these PnC GaN resonators exhibit record-breaking power handling, with IIP3 of +27.2dBm demonstrated at 993MHz.